The Collaborative International Dictionary of English v.0.48:

Barometer \Ba*rom"e*ter\, n. [Gr. ba`ros weight + -meter: cf. F.
   barom[`e]tre.]
   An instrument for determining the weight or pressure of the
   atmosphere, and hence for judging of the probable changes of
   weather, or for ascertaining the height of any ascent.
   [1913 Webster]

   Note: The barometer was invented by Torricelli at Florence
         about 1643. It is made in its simplest form by filling
         a graduated glass tube about 34 inches long with
         mercury and inverting it in a cup containing mercury.
         The column of mercury in the tube descends until
         balanced by the weight of the atmosphere, and its rise
         or fall under varying conditions is a measure of the
         change in the atmospheric pressure. At the sea level
         its ordinary height is about 30 inches (760
         millimeters). See Sympiesometer. --Nichol.
         [1913 Webster]

   Aneroid barometer. See Aneroid barometer, under
      Aneroid.

   Marine barometer, a barometer with tube contracted at
      bottom to prevent rapid oscillations of the mercury, and
      suspended in gimbals from an arm or support on shipboard.


   Mountain barometer, a portable mercurial barometer with
      tripod support, and long scale, for measuring heights.

   Siphon barometer, a barometer having a tube bent like a
      hook with the longer leg closed at the top. The height of
      the mercury in the longer leg shows the pressure of the
      atmosphere.

   Wheel barometer, a barometer with recurved tube, and a
      float, from which a cord passes over a pulley and moves an
      index.
      [1913 Webster] Barometric

WordNet (r) 3.0 (2006):

barometer
    n 1: an instrument that measures atmospheric pressure

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "barometer":
   aerological instrument, aneroid barometer, aneroidograph,
   barograph, barometrograph, canon, check, criterion, degree, feeler,
   gauge, glass, graduated scale, hurricane-hunter aircraft,
   hygrometer, measure, model, norm, parameter, pattern,
   pilot balloon, probe, quantity, radiosonde, random sample, reading,
   readout, recording barometer, rule, sample, scale, sound, sounder,
   standard, straw vote, test, touchstone, trial balloon, type,
   vacuometer, value, weather balloon, weather instrument,
   weather satellite, weather vane, weathercock, weatherglass,
   yardstick



The Devil's Dictionary (1881-1906):

BAROMETER, n.  An ingenious instrument which indicates what kind of
weather we are having.